The long-term goal of this research is to characterize two membrane transport systems involved in the regulation of intracellular pH in an established line of kidney epithelial cells (LLC-PK1): the amiloride-sensitive Na/H exchanger and the DIDS-sensitive Cl/HCO3 exchanger. Mutants defective in each of these transport systems have already been isolated, and will be characterized by isotope flux studies and by optical measurements of pH, both at the whole-cell level and in isolated membrane vesicles. The mutants will be used in physiological studies to investigate the relative roles of the Na/H and Cl/HCO3 exchangers in controlling pH during growth and differentiation. They will also be used to identify the transport proteins and to clone the corresponding genes. The proposed studies should contribute to our understanding of the physiology and pathophysiology of the proximal tubule and other leaky epithelia. They should also shed light on such fundamental processes as the regulation of intracellular pH and the control of cell proliferation.